Testosterone is an essential androgen hormone that is produced by both men and women. Women produce testosterone in the ovaries and adrenal glands, but men produce testosterone at a much greater level through the testicles. As testosterone is more present in men than women, it has certain unique effects on the human male body as it is released into the bloodstream.
Testosterone first acts on the human male during the prenatal growth process. It is testosterone that is largely responsible for activating the formation of male-specific body parts during development in the womb such as the penis, scrotum and prostate.
Testosterone's next largest portion of time where it affects men is during puberty. In puberty, testosterone levels increase in boys, causing more manly characteristics to develop such as body hair, pubic hair, penis growth, testicle growth, voice lowering and the production of sperm. During this time testosterone may also influence an increase in penile erections, as well as the spontaneous ejection of semen, commonly referred to as "nocturnal emissions" or "wet dreams".
Testosterone may also change the overall physical appearance of a man during puberty. This usually entails the growth of a more prominent Adam's apple, as well as a change in the bone contours of the jaw, face and eyebrows, providing more manly features. Testosterone also activates an increase in the length of the bones, increasing overall height.
Testosterone affects the male's abilities to function sexually. Testosterone plays a role in fertility, libido, semen production, penile erection, and ejaculation, making procreation possible. Testosterone makes this process possible during puberty, and continues to control sexual function through the rest of your adult life.
Testosterone also has anabolic properties in men. These anabolic properties cause an increase in bone and muscle mass, providing additional strength and structure to men over women who have less natural testosterone. Anabolic steroids mimic the anabolic effects of testosterone, which is what causes the increased bone and muscle size in both men and women using the drug.